Improvement in screw-taps



S. W. MARTIN.

SCREW-TAP. 7 No. 177,731. Patented May 23,1876.

247mm,. Invenfir: g gj NJEIYERS, PHOTO-LITNOGRAPHER, WASHINGTON. D. C.

- the tap is made. forged into shape as it is before the teeth areUNITED STATES PATENT OFFICE.

SAMUEL -W. MARTIN, OF SPRINGFIELD, OHIO, ASSIGNOR OF ONE-HALF HIS VRIGHTTO PHINEAS P. MAST, OF SAME PLACE.

IMPROVEMENT IN SCREW-TAPS.

Specification forming part of Letters Patent No. 177,73 1, dated May 23,1876 application filed May 3, 1876.

in Taps for Cutting Screw-Threads, of which the following is aspecification:

My invention consistsiief a tap for cutting screw-threads, having twoflat sides with the teeth out on the opposite edges, as hereinafter morefully set forth. I I

Figure 1 represents the blank from which Fig. 2represents the same out.Fig.- 3 is a perspective view of the tap as it is when finished readyfor use. Fig. 4 is a transverse section of the same, and Fig. 5 atransverse section of the tap slightly modified by making the sidesconcave;

The object of my present invention is to produced in thicknesss aboutone-third, the metal thus displaced being forced out atthe edges,thereby increasing its width proportionately, care being taken in thisoperation to make it where it is squared, to enable it to be fitted inand held by a wrench or other tool when in use. After being thus formedit has teeth 0 cut on its two edges, which are left or formed in the arcof a circle, as shown inFig. 4. It is then tempered and is'ready foruse. ferred its sides may be made concave, as shown inFig. 5, by which alittlewmore rake is given to the front edges of the teeth, but this I donot find necessary,- as I find the flat sides to work well in practice.When the tap becomes dull from use all that is necessary in in order tosharpen it is to grind the flat sides, which can be done on an ordinarygrindstone.

This plan of constructing taps is exceeding- ]ysimple and cheap, and atap thus made operates in a most satisfactory manner, and'one of itsgreat advantages is the ease with whlch.

it can be' sharpened.

I am aware that a tap has been made round with longitudinal groovesinits sides, and I do not claim such; but

What I do claim 'is-- A screw-cutting tap, consisting of a round rodflattened on its sides, having teeth formed on the edges thereof, asshown and described.

SAMUEL W. MARTIN. Witnesses:

\ J. J. HAMA,

' OSCAR S. MARTIN."

If pre

